Chain of fiber-reinforced resin composite material

ABSTRACT

A chain formed of links made of fiber-reinforced resin composite material. Each link has a terminal loop located at each axial end of a long strap. Loops, located at adjacent ends of successive links, are joined by relatively short connecting links that overlap bushings located within each of the loops. The bushings and connecting links are held in position at each lateral side of the links by pins and washers. A ring surrounds each link where the strap flares to form each terminal loop. The loops may be unitary or spaced laterally to receive within the space a unitary loop of an adjoining link aligned axially with the other loop. A pin located within the loops supports washers at each lateral side of the links to maintain the position of the links and to transfer load between the links.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of chain and chain links, especiallylong, high strength chin for mooring lines and tension legs used toconnect offshore platforms to the sea floor. The invention pertains tosuch chain formed of synthetic materials, especially to a composite thatincludes plastic resin reinforced with high strength fibers.

2. Description of the Prior Art

Conventional mooring lines and tension legs are made from steel rope orcable having a diameter of five to six inches. In service they carrytensile loads for long periods while submerged in sea water. But theweight of steel in sea water is 92 percent of its weight in air.Therefore, due to the great size, length and weight of conventionalsteel cables, offshore platforms fixed to the sea floor by such cablesmust be larger than otherwise required so they can buoy the lines. Useof tubular cables of composite material to reduce weight of mooringlines is described in U.S. Pat. No. 4,589,801.

An articulated riser supporting multiple fluid handling lines extendingbetween a structure on the sea bottom and a surface vessel is describedin U.S. Pat. No. 4,031,919. Adjacent segments of the riser are joinedmutually by a universal joint, which provides axial force continuitybetween the riser segments while permitting relative pivotal movementbetween them.

Various techniques, employed to connect long, flexible lengths of belt,cable and filament, to form longer lengths and endless belts are known.The cable loop connector described in U.S. Pat. No. 4,150,906 releasablyjoins loops located at the ends of cables. The connector carrying ahook, is fastened to a first cable by sliding a tapered portion of thecable through a tapered opening such that the first cable extends beyondthe connector and loops back to engage the hook. The loops of adjacentcables so arranged are looped together to connect the cables.

A spiral seam for joining the ends of a Papermaker's fabric is describedin U.S. Pat. No. 4,862,926. Yarn is looped over pintles, which alsoconnect coiled members to the yarn, at adjacent ends of the fabric. Thecoiled members of each fabric are aligned and interleaved mutually withthe coiled members at the end of the adjacent fabric. Then anotherpintle passes through aligned loops formed in the coils to connect thefabrics.

The free ends of belts are connected to make endless belts by passing apin or link between loops fixed to the belt ends, as shown in U.S. Pat.No. 2,185,563. Belt ends are connected also by fixing to each belt end aclamp having a loop facing the other free end. A bearing having atransverse hole is located within each clamp. Then links, located atopposite lateral sides of the belt and having axially spaced holes, arearranged so that the holes of the links and bearings are aligned.Finally, pintles are inserted through the holes of the links andbearings to connect the belt ends. A device of this type is described inU.S. Pat. No. 2,675,592.

The enormous length and great size of conventional mooring lines andtension legs makes transport and placement of them difficult. Typicallythey are transported by rail to a shoreline, fitted with flotation gearand towed to the offshore service site. If their weight and bulk couldbe reduced substantially and their ability to be lengthened andshortened readily could be improved, then they could be assembled to apredetermined length and towed with minimum flotation support to theoffshore site.

SUMMARY OF THE INVENTION

A need exists for light weight chain for connecting offshore drillingplatforms to the sea floor having strength sufficient to withstand largeloads for long periods, improved ease of assembly and disassembly, andtolerance to an underwater environment.

The weight of composite materials in air is one-quarter the weight ofsteel in air and nearly one-eighth the weight of steel in sea water.Moreover, the tensile strength of composite materials is approximatelythe same as that of steel. However, the greatest strength of compositematerials results when the direction of the fibers is in the directionof the load. Therefore, when the principal load is tensile and directedalong the length of a structural member, maximum strength and minimumweight result when the fiber direction is longitudinal. When the chainlinks are metallic, they can be interconnected by conventionaltechniques such as those that involve drilling holes through loadcarrying structural members, aligning the holes and connecting themembers by placing a pin in the aligned holes.

This practice is unacceptable where composite materials are used,especially where the fiber direction is unidirectional, because drillingholes severs the highly loaded fibers and requires redistribution ofload within the composite matrix adjacent each hole. Furthermore,unidirectional composite material has relatively low shear strengthparallel to the fiber direction, which is the mode and directional senserequired to transfer load in the matrix between the composite materialand connecting pins, if they were used. Therefore, the chain of thisinvention maximizes the high tensile strength capability ofunidirectional fiber composite material and avoids link-to-linkattachments that cause large stresses in the composite matrix indirections having inherently low strength.

It is an object of this invention to provide relatively light weightchain of composite material, whose links can be readily assembled anddisassembled without compromising strength and weight advantages of thematerial.

It is another object that the connection between successive links beefficient and compatible with the unique stiffness and strengthproperties of composite materials. The chain of this invention can befabricated at low cost by filament winding material and processes thatpermit use of various combinations of fiber materials and resins torealize the advantages of high strength, stiffness and low cost.

It is a further object that this invention will permit the chain totransition easily to steel chain for use with a tensioning winch locatedat the water surface.

In realizing these objectives the chain of this invention is fabricatedof fiber-reinforced resin composite material. Each link has a terminalloop located at each axial end of a long strap. Loops, located atadjacent ends of successive links, are joined by relatively shortconnecting links that overlap bushings located within each of the loops.The bushings and connecting links are held in position at each lateralside of the links by pins and washers. A ring surrounds each link wherethe strap flares to form each terminal loop. The loops of a link may beunitary or in two Portions spaced laterally to receive within the spacea unitary loop of an adjoining link, aligned axially with the otherspaced loops. A pin located within the loops supports washers at eachlateral side of the links to maintain the position of the links and totransfer load between the links.

These objects and other objects, features and advantages of theinvention are readily apparent from the following detailed descriptionof the best mode for carrying out the invention when taken in connectionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a isometric view illustrating joined links of a compositechain according to the invention, each link having a terminal loop.

FIG. 2 shows, in laterally spaced relationship, the components of thejoint that connects the links of FIG. 1.

FIG. 3 is a side view of the assembly of FIG. 1.

FIG. 4 is a cross section taken at plane 4--4 of FIGS. 3 and 7illustrating a ring surrounding each link.

FIG. 5 is an isometric view illustrating joined links of a compositechain in accordance with the invention, each link having a single loopedend and a multiple looped end.

FIG. 6 shows, in laterally spaced relationship, the components thatconnect the links of FIG. 5, the links being mutually offsetlongitudinally from their assembled position.

FIG. 7 is a side view of the assembly of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawing figures, there is illustrated in FIGS. 1-4chain links and components for connecting successive links for easyassembly and disassembly. Substantially identical links 10, 11, each upto 100 feet long, are fabricated from composite material, principallyepoxy resin reinforced by high strength fibers such as fiberglass orgraphite, also called carbon fiber. The load carried by the links isprincipally tensile; therefore, the reinforcing fiber of the links ispredominantly unidirectional and directed longitudinally, parallel tothe length of the links. The tensile strength of such unidirectionalcomposite material when loaded in the direction of fibers isapproximately the same as that of high strength alloy steel, yet itsdensity is about one-quarter that of steel.

The links are fabricated with filament windings comprising a substantialthickness of unpolymerized or partially polymerized epoxy or othersuitable resin containing a matrix of long, thin closely spaced fibersdirected substantially along the length of the link. Virtually theentire surface of each fiber is wetted by the resin. Generally, suitablesteps are taken to minimize the volume of air entrapped within thecomposite matrix. The length, width and thickness of the links aredetermined by the service requirements of the chain, usually bystrength, and the shape of the links is determined by the shape of amold or other form into which the sized filament winding is placed whilethe resin is unpolymerized and still plastic. Then, the resin ispolymerized by heating, thereby solidifying the composite matrix andfixing its shape to that of the mold.

Each link includes a substantially planar, endless strap 12, 13 and twoloops 14-17, which flare laterally outward and terminate at cylindricalsurfaces 18. Two rings 20 surrounding each strap are located at thepoints where each strap flares to form the terminal loops. The rings 20,shown in cross section in FIG. 4, include spacers 22 having a flat innersurface contacting the strap and a semicircular outer surface, and anouter winding 24 of composite material such as resin reinforced by fiberglass or graphite fiber. The rings provide against the possibility thatthe strap might separate at its mid-plane due to the presence of acomponent of force directed out of plane at the location of the ringswhere the loops flare outward from the plane of the strap. The restraintprovided by the rings induces a hoop load in the rings; therefore, theprincipal direction of the reinforcing fiber of the rings iscircumferential.

A bushing 26, 28 of steel or composite material, having an outer surfaceconforming substantially to the inner surface of the loops, is locatedin each adjacent loop 15, 16 of aligned successive links 10, 11. Theouter surface of each bushing comprises first and second arcuatesurfaces 27, 29 mutually spaced longitudinal and elongated surfaces 31located between the first and second arcuate surfaces (FIG. 2). Thelength of the bushings is longer than the lateral width of the loops andextends beyond each lateral side of the loops. A connecting link 30, 32,preferably of resin reinforced by fiber glass or graphite fibersdirected around the circumference of the connecting loops, overlaps theouter surface of the bushings 26 and 28, thereby connecting the bushingsand associated loops against outward axial movement. The outercylindrical surfaces of the loops 15, 16 are located in close mutualproximity, thereby preventing inward relative axial displacement of theloops.

A headed pin 34, 36 carrying a washer 38, 40, adapted to contact thelateral surfaces of the connecting link 30 and bushings 26, 28, extendslaterally through each bushing and connecting link 30, 32 and presents aportion of its surface at the opposite lateral side of the links fromthat of the pin head. There, a washer 42, 44 is placed on each pin closeto, or into contact with the adjacent lateral surfaces of the bushingsand the connecting link 32. A cotter pin 46, 48 fixed to each pin 34, 36holds washers 42, 44 against the connecting link 32 and bushings, andprevents displacement of the pins.

FIGS. 5-7 show another embodiment in which each link has a terminal loop16 of the type described above and, located at the opposite end of thelink, two loops 50, 52 spaced laterally and aligned mutually about alateral axis. The spacing between loops 50, 52 is sufficient to receivebetween them the single loop 16 of the next link 13.

Connection of links 10 and 11 requires aligning the loops 50, 16, 52about the lateral axis with loop 16 between the other loops 50 and 52. Aheaded pin 54 carrying a washer 56, adapted to contact the lateralsurfaces of link 50 extends laterally through loops 50, 16, and 52 andpresents a portion of its surface at the opposite lateral side of loop52 from that of the pin head. There, a washer 58 is placed on the pin incontact with the adjacent lateral surface of loop 52. A cotter pin 60,fixed to pin 54, holds the washers against loops 50 and 52 and preventsdisplacement of the pin.

While the best mode for carrying out the invention has been described indetail, those familiar with the relevant art will recognize variousalternative designs and embodiments for practicing the invention definedby the following claims.

What is claimed is:
 1. A chain of joined links for supporting orrestraining objects, at each joint the chain comprising:first and secondlongitudinally extending links, each link having a loop at each end; afirst bushing located within the loop of the first link and extendinglaterally therefrom; a second bushing located within the loop of thesecond link and extending laterally therefrom; a first connecting linklocated at a first lateral side of the loops of the first and secondlinks, contacting the first bushing and second bushing; a secondconnecting link located at a second lateral side of the loops of thefirst and second links, contacting the first bushing and second bushing;a first pin extending laterally through the first bushing, and a secondpin extending laterally through the second bushing, each pin carryingblocking surfaces adjacent the first and second connecting links and thefirst and second bushings; and means for securing the position of thepins and limiting movement of the bushings and connecting links mutuallyand relative to the loops of the first and second links, wherein thelinks are of composite material having fiber-reinforced plastic resin,the fibers are of the group consisting of fiberglass, carbon andgraphite, and the fibers are directed substantially parallel to thelength of the links.
 2. The chain of claim 1 wherein the first link andsecond link each comprises:a longitudinally extending strap havinglateral material width and transverse material thickness; a first loopextending longitudinally from the strap in a first direction and asecond loop extending longitudinally from the strap in a seconddirection opposite the first direction, each loop extending transverselyoutward from the strap, and having a material thickness substantiallyequal to one-half the material thickness of the strap and a materialwidth substantially the same as that of the strap.
 3. The chain of claim2 wherein the strap is substantially planar and each loop extendstransversely outward from the plane of the strap, and further comprisingfirst and second rings surrounding the strap, the first ring located ata juncture of the first loop and the strap, the second ring located at ajuncture of the second loop and the strap.
 4. A chain of joined linksfor supporting or restraining objects, at each joint the chaincomprising:first and second longitudinally extending links, each linkhaving a loop at each end; first bushing means located within the loopof the first link for resisting longitudinal movement of the first linkrelative to the second link; second bushing means located within theloop of the second link for resisting longitudinal movement of thesecond link relative to the first link; first means located at a firstlateral side of the links for mutually connecting the first bushingmeans and second bushing means; second means located at a second lateralside of the links for mutually connecting the first bushing and thesecond bushing; and pin means extending laterally through the firstbushing and second bushing for limiting movement of the bushings andconnecting links mutually relative to the loops of the first link andsecond link, wherein the links are of composite material havingfiber-reinforced plastic resin, the fibers are of the group consistingof fiberglass, carbon and graphite, and the fibers are directedsubstantially parallel to the length of the links.
 5. A chain of joinedlinks for carrying tension load between objects restrained by the chain,at each joint the chain comprising:first and second longitudinallyextending links, each link carrying tension force and having a loop ateach end; first bushing means located within the loop of the first linkfor resisting tension force carried by the first link; second bushingmeans located within the loop of the second link for resisting tensionforce carried by the second link; first connecting means located at afirst lateral side of the links, overlapping the first and secondbushing means, for balancing tension force in the first link and secondlink; a second connecting link located at a second lateral side of thelinks, overlapping the first and second bushing means, for balancingtension force in the first link and second link; and pin means extendinglaterally through the first bushing means and second bushing means forlimiting movement of said first and second bushing means and theconnecting links mutually relative to the loops of the first link andsecond link, wherein the links are of composite material havingfiber-reinforced plastic resin, the fibers are of the group consistingof fiberglass, carbon and graphite, and the fibers are directedsubstantially parallel to the length of the links.
 6. A chain linkcomprising:a longitudinally extending, substantially planar strap havinglateral material width and transverse material thickness; a first loopextending longitudinally from the strap in a first direction and asecond loop extending longitudinally from the strap in a seconddirection opposite the first direction, each loop extending transverselyoutward from the strap and having a material thickness substantiallyequal to one-half the material thickness of the strap and a materialwidth substantially the same as that of the strap, the first and secondloops having inner arcuate surfaces; and first and second ringssurrounding the strap, the first ring located at a juncture of the firstloop and the strap, the second ring located at a juncture of the secondloop and the strap.
 7. A chain link comprising:a longitudinallyextending, substantially planar strap having lateral material width andtransverse material thickness; a first loop extending longitudinallyfrom the strap in a first direction and a pair of laterally spaced loopsextending longitudinally from the strap in a second direction oppositethe first direction, each loop extending transversely outward from thestrap and having a material thickness substantially equal to one-halfthe material thickness of the strap, the first loop having a materialwidth substantially the same as that of the strap, the pair of loopshaving a combined material width substantially the same as that of thestrap; and first and second rings surrounding the strap, the first ringlocated at a juncture of the first loop and the strap, the second ringlocated at a juncture of the pair of loops and the strap.
 8. The chainof claim 7 wherein the links are of composite material havingfiber-reinforced plastic resin, the fibers are of the group consistingof fiberglass, carbon and graphite, the fibers being directedsubstantially parallel to the length of the links.
 9. A chain of joinedlinks for supporting or restraining objects, at each joint the chaincomprising:first and second longitudinally extending links, each linkhaving a loop at each end; a first bushing means located within the loopof the first link and extending laterally therefrom; a second bushingmeans located within the loop of the second link and extending laterallytherefrom; a first connecting link located at a first lateral side ofthe loops of the first and second links, contacting the first bushingand second bushing; a second connecting link located at a second lateralside of the loops of the first and second links, contacting the firstbushing and second bushing; a first pin extending laterally through thefirst bushing, and a second pin extending laterally through the secondbushing, each pin carrying blocking surfaces adjacent the first andsecond connecting links and the first and second bushings; and means forsecuring the position of the pins and limiting movement of the bushingsand connecting links mutually and relative to the loops of the first andsecond links, wherein a loop of the first link is longitudinally alignedwith a loop of the second link, each bushing having outer surfacescomprising first and second arcuate surfaces mutually spacedlongitudinally, and surfaces located between the first and secondarcuate surfaces, the loops of the first and second links having innersurfaces conforming to the first arcuate surface, the first and secondconnecting links having an inner surface overlapping and conformingsubstantially to the second arcuate surface.
 10. A chain of joined linksfor supporting or restraining objects, at each joint the chaincomprising:first and second longitudinally extending links, each linkhaving a loop at each end; a first bushing located within the loop ofthe first link and extending laterally therefrom; a second bushinglocated within the loop of the second link and extending laterallytherefrom; a first connecting link located at a first lateral side ofthe loops of the first and second links, contacting the first bushingand second bushing; a second connecting link located at a second lateralside of the loops of the first and second links, contacting the firstbushing and second bushing; a first pin extending laterally through thefirst bushing, and a second pin extending laterally through the secondbushing, each pin carrying blocking surfaces adjacent the first andsecond connecting links and the first and second bushings; and means forsecuring the position of the pins and limiting movement of the bushingsand connecting links mutually and relative to the loops of the first andsecond links, said securing and limiting means comprising: first andsecond washers carried on the pins, located at said first lateral sidebetween the blocking surfaces of the pins and the bushings andconnecting links; a securing pin carried on each pin, directed laterallythereto and located at said second lateral side; and third and fourthwashers, each carried on a pin, located at said second lateral sidebetween a securing pin and the bushings and connecting links.
 11. Achain of joined links for supporting or restraining objects, at eachjoint the chain comprising:first and second longitudinally extendinglinks, each link having a loop at each end; a first bushing meanslocated within the loop of the first link and extending laterallytherefrom; a second bushing located within the loop of the second linkand extending laterally therefrom; a first connecting link located at afirst lateral side of the loops of the first and second links,contacting the first bushing and second bushing; a second connectinglink located at a second lateral side of the loops of the first andsecond links, contacting the first bushing and second bushing; a firstpin extending laterally through the first bushing, and a second pinextending laterally through the second bushing, each pin carryingblocking surfaces adjacent the first and second connecting links and thefirst and second bushings; and means for securing the position of thepins and limiting movement of the bushings and connecting links mutuallyand relative to the loops of the first and second links, wherein thelinks are of composite material having fiber-reinforced plastic resin,the fibers are of the group consisting of fiberglass, carbon andgraphite, the fibers being directed substantially parallel to the lengthof the links.
 12. A chain of joined links for supporting or restrainingobjects, at each joint the chain comprising:first and secondlongitudinally extending links, each link having a loop at each end; afirst bushing means located within the loop of the first link andextending laterally therefrom; a second bushing located within the loopof the second link and extending laterally therefrom; a first connectinglink located at a first lateral side of the loops of the first andsecond links, contacting the first bushing and second bushing; a secondconnecting link located at a second lateral side of the loops of thefirst and second links, contacting the first bushing and second bushing;a first pin extending laterally through the first bushing, and a secondpin extending laterally through the second bushing, each pin carryingblocking surfaces adjacent the first and second connecting links and thefirst and second bushings; and means for securing the position of thepins and limiting movement of the bushings and connecting links mutuallyand relative to the loops of the first and second links, wherein thelinks and the first and second connecting links are of compositematerial having fiber-reinforced plastic resin, the fibers are of thegroup consisting of fiberglass, carbon and graphite, the fibers beingdirected substantially parallel to the length of the links.
 13. A chainof joined links for supporting or restraining objects, at each joint thechain comprising:first and second longitudinally extending links, eachlink having a loop located at a first end and a pair of laterally spacedloops located at a second end, the loop of the first link locatedbetween the pair of loops of the second link; a pin having a laterallydirected axis, located within and contacting the loop of the first linkand the pair of loops of the second link; and means for securing theposition of the pin and limiting movement of the first link relative tothe loops of the first and second links, said pin comprising: first andsecond arcuate surfaces mutually spaced longitudinally; and surfaceslocated between the first and second arcuate surfaces, the loop of thefirst link having an inner surface overlapping and conformingsubstantially to the first arcuate surface, the pair of loops of thesecond link having an inner surface overlapping and conformingsubstantially to the second arcuate surface.
 14. A chain of joined linksfor supporting or restraining objects, at each joint the chaincomprising:first and second longitudinally extending links, each linkhaving a loop located at a first end and a pair of laterally spacedloops located at a second end, the loop of the first link locatedbetween the pair of loops of the second link; a pin having a laterallydirected axis, located within and contacting the loop of the first linkand the pair of loops of the second link, said pin having a blockingsurface thereon; and means for securing the position of the pin andlimiting movement of the first link relative to the loops of the firstand second links, said securing and limiting means comprising: first andsecond washers carried on the pin, the first washer located at a firstlateral side between the blocking surface and one of the pair of loopsof the second link, the second washer located at a second lateral sideadjacent the other of the pair of loops of the second link; and securingmeans for limiting movement of the pin.
 15. A chain of joined links forsupporting or restraining objects, at each joint the chaincomprising:first and second longitudinally extending links, each linkhaving a loop located at a first end and a pair of laterally spacedloops located at a second end, the loop of the first link locatedbetween the pair of loops of the second link; a pin having a laterallydirected axis, located within and contacting the loop of the first linkand the pair of loops of the second link; and means for securing theposition of the pin and limiting movement of the first link relative tothe loops of the first and second links, wherein the first and secondlinks each comprising: a longitudinally extending strap having lateralwidth and transverse thickness; a first loop extending longitudinallyfrom the strap in a first direction and a pair of laterally spaced loopsextending longitudinally from the strap in a second direction oppositethe first direction, each loop extending transversely outward from thestrap and having a thickness substantially equal to one-half thethickness of the strap, the first loop having a width substantially thesame as that of the strap, the pair of loops having a combined widthsubstantially the same as that of the strap.
 16. The chain of claim 15wherein the strap is substantially planar and each loop extendstransversely outward from the plane of the strap, and further comprisingfirst and second rings surrounding the strap, the first ring located ata juncture of the first loop and the strap, the second ring located at ajuncture of the pair of loops and the strap.
 17. A chain linkcomprising:a longitudinally extending, substantially planar strap havinglateral width and transverse thickness; a first loop extendinglongitudinally from the strap in a first direction and a second loopextending longitudinally from the strap in a second direction oppositethe first direction, each loop extending transversely outward from thestrap having a thickness substantially equal to one-half the thicknessof the strap and a width substantially the same as that of the strap,the first and second loops having inner arcuate surfaces; and first andsecond rings surrounding the strap, the first ring located at a junctureof the first loop and the strap, the second ring located at a junctureof the second loop and the strap, wherein the links are of compositematerial having fiber-reinforced plastic resin, the fibers are of thegroup consisting of fiberglass, carbon and graphite, the fibers beingdirected substantially parallel to the length of the links.